Isobutanol

Isobutanol (IUPAC nomenclature: 2-methylpropan-1-ol) is an organic compound with the formula (CH₃)₂CHCH₂OH (sometimes represented as i-BuOH). This colorless, flammable liquid with a characteristic smell is mainly used as a solvent either directly or as its esters. Its isomers are 1-butanol, 2-butanol, and tert-butanol, all of which are important industrially.^[5]

Isobutanol (2-Methyl-propan-1-ol)

Skeletal formula of isobutanol
Ball-and-stick model of isobutanol
Names
Preferred IUPAC name 2-Methylpropan-1-ol
Other names Isobutyl alcohol IBA 2-Methyl-1-propanol 2-Methylpropyl alcohol Isopropylcarbinol
Identifiers
CAS Number	78-83-1 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1730878
ChEBI	CHEBI:46645 Y
ChEMBL	ChEMBL269630 Y
ChemSpider	6312 Y
ECHA InfoCard	100.001.044
EC Number	201-148-0
Gmelin Reference	49282
KEGG	C14710 Y
PubChem CID	6560
RTECS number	NP9625000
UNII	56F9Z98TEM Y
UN number	1212
CompTox Dashboard (EPA)	DTXSID0021759
InChI InChI=1S/C4H10O/c1-4(2)3-5/h4-5H,3H2,1-2H3 Y Key: ZXEKIIBDNHEJCQ-UHFFFAOYSA-N Y InChI=1/C4H10O/c1-4(2)3-5/h4-5H,3H2,1-2H3
SMILES CC(C)CO
Properties[1]
Chemical formula	C4H10O
Molar mass	74.122 g/mol
Appearance	Colorless liquid
Odor	sweet, musty[2]
Density	0.802 g/cm3, liquid
Melting point	−108 °C (−162 °F; 165 K)
Boiling point	107.89 °C (226.20 °F; 381.04 K)
Solubility in water	8.7 mL/100 mL[3]
log P	0.8
Vapor pressure	9 mmHg (20°C)[2]
Refractive index (nD)	1.3959
Viscosity	3.95 cP at 20 °C
Hazards[1]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H315, H318, H335, H336
Precautionary statements	P210, P233, P240, P241, P242, P243, P261, P264, P271, P280, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P332+P313, P362, P370+P378, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)	1 3 0
Flash point	28 °C (82 °F; 301 K)
Autoignition temperature	415 °C (779 °F; 688 K)
Explosive limits	1.7–10.9%
Lethal dose or concentration (LD, LC):
LDLo (lowest published)	3750 mg/kg (rabbit, oral) 2460 mg/kg (rat, oral)[4]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 100 ppm (300 mg/m3)[2]
REL (Recommended)	TWA 50 ppm (150 mg/m3)[2]
IDLH (Immediate danger)	1600 ppm[2]
Safety data sheet (SDS)	ICSC 0113
Related compounds
Related butanols	1-Butanol sec-Butanol tert-Butanol
Related compounds	Isobutyraldehyde Isobutyric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

History and occurrence

Fusel alcohols including isobutanol are grain fermentation byproducts. Therefore, trace amounts of isobutanol may be present in many alcoholic beverages.

In 1852 Charles Adolphe Wurtz subjected such alcohols to fractional distillation and identified in some of them a butylic alcohol boiling at around 108°C.^[6] Its structure was initially unclear, with some chemists believing it corresponded to butyric acid, but theoretical considerations indicated that normal butanol should have a higher boiling point, and in 1867 Emil Erlenmeyer and independently Vladimir Markovnikov determined its actual structure by proving its oxidation product to be isobutyric acid.^[7][8]

Production

Isobutanol is produced by the carbonylation of propylene. Two methods are practiced industrially, hydroformylation is more common and generates a mixture of isobutyraldehyde and butyraldehyde:

CH₃CH=CH₂ + CO + H₂ → CH₃CH₂CH₂CHO

The reaction is catalyzed by cobalt or rhodium complexes. The resulting aldehydes are hydrogenated to the alcohols, which are then separated. In Reppe carbonylation, the same products are obtained, but the hydrogenation is effected by the water-gas shift reaction.^[5]

Laboratory synthesis

Propanol and methanol can be reacted to produce isobutyl alcohol via Guerbet condensation.^[9]

Biosynthesis of isobutanol

Main article: Butanol fuel

E. coli as well as several other organisms has been genetically modified to produce C4 alcohols from glucose, including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethanol. The host's highly active amino acid biosynthetic pathway is shifted to alcohol production. α-Ketoisovalerate, derived from valine, is prone to decarboxylation to give isobutyraldehyde, which is susceptible to reduction to the alcohol:^[10]

(CH₃)₂CHC(O)CO₂H → (CH₃)₂CHCHO + CO₂

(CH₃)₂CHCHO + NADH + H⁺ → (CH₃)₂CHCH₂OH + NAD⁺

Applications

The uses of isobutanol and 1-butanol are similar. They are often used interchangeably. The main applications are as varnishes and precursors to esters, which are useful solvents, e.g. isobutyl acetate. Isobutyl esters of phthalic, adipic, and related dicarboxylic acids are common plasticizers.^[5] Isobutanol is also a component of some biofuels.^[11]

Safety and regulation

Isobutanol is one of the least toxic of the butanols with an LD₅₀ of 2460 mg/kg (rat, oral).^[5]

In March 2009, the Government of Canada announced a ban on isobutanol use in cosmetics.^[12]